1. Field of the Invention
This invention generally relates to electrical switching devices and more particularly to switching devices of the single in-line package type.
2. Description of Related Art
Single in-line package (SIP) switches have many applications, particularly in electronic circuitry used in digital data processing systems and like products. For example, such products often include groups of termination resistors connected to various signal lines. Each termination resistor connects between a signal line and a fixed potential (typically +5 VDC). A switch then couples the common connection of the termination resistor and signal line to a ground potential. When the switch is open, the signal line floats at the positive potential. When the switch closes, the signal line is clamped at ground potential.
Different switching alternatives exist for such applications especially when the signal lines are logically related. As an example, a group of four signal lines and switches can collectively set a baud rate for data transmission. In accordance with one alternative a 4.times.4 matrix of eyelets could be formed on a printed circuit board. Conduct runs could connect a first row to a positive reference potential; the fourth row, to ground. The eyelets in each column of the second and third rows would connect to a corresponding signal line and to each other. The termination resistors would be inserted between the corresponding eyelets in the first and second rows. Individual switching devices then could be inserted between the corresponding eyelets in the third and fourth rows. Thus, this arrangement allows the state of each signal line to be controlled individually.
As another alternative, a four-pole dual in-line package (DIP) switch could be substituted for the individual switches. This simplifies manufacturing assembly because one component is substituted for four individual switches. However, a DIP switch requires approximately the same area on the printed circuit board as four individual switches. Secondly, the individual poles in a DIP switch are independent switches that incorporate separate, isolated switch mechanisms. This increases the cost of implementing the switching function in many applications.
SIP switches can provide more switch contacts than a DIP switch in a given printed circuit board area. Prior art SIP switches often include an insulating base and a cavity for housing a self-contained switching mechanism including two spaced contacts, a bridging contact and a detent mechanism for permitting an individual to "feel" the switch move between the open and closed positions.
U.S. Pat. No. 4,399,336 describes one such miniature rotary SIP switch for mounting on a printed circuit board. In this SIP switch, each pole has oppositely disposed contact leaf portions extending through a housing with an exterior terminal section and interior cantilevered switching section. A rotor disposed between contact portions of the interior switching sections can rotate between first and second positions. In a first position, a diametrically extending contact pin engages the contact portions of both leaf springs. The contact portions have dimples that coact with the contact pin to provide a detent when the switch turns on. In the second position the rotor interposes an insulating path between the contact leaves. Moreover, molded detent protrusions engage the dimples to provide a detent in this position. Each pole is self contained; the poles and terminal pairs for each pole are in a single line. As this switch includes independent switching structures at each pole position, it can be overly expensive for many applications. Although such switches improve switch density on the printed circuit board, even greater densities are necessary and desirable, especially as other component densities increase.